The effect of nanoprecipitates on the superelastic properties of FeNiCoAlTa shape memory alloy single crystals
The effect of nanoprecipitates on the superelastic properties of FeNiCoAlTa shape memory alloy single crystals
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DOI：
10.1016/j.actamat.2013.02.036
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发表时间：
2013-05-01
期刊：
影响因子：
9.4
通讯作者：
Chumlyakov, Y. I.
中科院分区：
文献类型：
--
作者：
Ma, Ji;Hornbuckle, B. C.;Chumlyakov, Y. I.
FeNiCoAlTa形状记忆合金具有高相变应变和高抗塑性变形性能。然而，从单晶观察到的相变应变比理论预测的要小得多，这可能与伽马‘(L1(2))析出物有关。因此，我们研究了纳米γ‘析出物对Fe-28%Ni-17%Co-11.5%Al-2.5%Ta单晶各种超弹性能的影响，发现它们对超弹性应力滞后、相变温度、应力温度相图以及沿<；100>；方向的应力应变响应特性都有深刻的影响。用三维原子探针层析技术定量测定了析出物的大小和体积分数，并首次确定了析出物的组成。在600℃以上时效7h后，析出相的体积分数几乎没有变化，但随着时效时间的延长，析出相粗化，化学成分略有变化，导致相变温度升高。此外，析出物尺寸的变化对拉伸和压缩超弹性行为的影响也不同。随着析出物尺寸的增大和数密度的减小，导致了超弹性特性的拉压不对称性，如可恢复性、应力滞后，并加剧了临界应力-温度斜率。我们根据拉伸和压缩超弹性实验中形成的马氏体的形态和变化结构的内在差异来解释这一观察结果。(C)2013 Acta Materialia Inc.由Elsevier Ltd.出版。保留所有权利。
FeNiCoAlTa shape memory alloys were recently discovered to possess a combination of high transformation strain and high resistance to plastic deformation. However, the transformation strain observed from single crystals is much smaller than theoretically predicted, which could be related to gamma' (L1(2)) precipitates. Therefore, we examined the effect of nanosized gamma' precipitates on various superelastic properties of Fe-28%Ni-17%Co-11.5%Al-2.5%Ta single crystals, and found that they have profound influence on the superelastic stress hysteresis, transformation temperatures, stress temperature phase diagram, and the characteristics of the stress strain response along the < 100 > orientations. The size and volume fractions of precipitates were determined quantitatively with 3-D atom probe tomography, and the composition of these precipitates was determined for the first time. Aging at 600 degrees C for 7 h and above resulted in little or no change in the volume fraction of the precipitates, but coarsening of the precipitates accompanied by modest changes in their chemical compositions was observed with increasing aging time, which resulted in an increase in the transformation temperatures. Furthermore, the change in the precipitate size affected tensile and compressive superelastic behavior differently. An increasing size of the precipitates, and thus decreasing number density, caused tension compression asymmetry in the superelastic characteristics, such as recoverability, stress hysteresis, and intensified the critical stress vs. temperature slope. We explain this observation based on the inherent differences in the morphology and variant structures of the martensite formed during tension and compression superelastic experiments. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.